compiletest: pass -Zunstable-options for unpretty and no-codegen paths

Unconditionally pass -Zunstable-options in the `unpretty` and
`-Zno-codegen` (typecheck) paths in compiletest. This ensures
custom targets resolved via RUST_TARGET_PATH work consistently.

This is primarily needed when using non-built-in targets without
a .json extension.

Signed-off-by: Deepesh Varatharajan <Deepesh.Varatharajan@windriver.com>

Author: DeepeshWR

src/tools/compiletest/src/runtest.rs

@@ -452,6 +452,7 @@ impl<'test> TestCx<'test> {
         rustc
             .arg(input)
             .args(&["-Z", &format!("unpretty={}", pretty_type)])
+            .arg("-Zunstable-options")
             .args(&["--target", &self.config.target])
             .arg("-L")
             .arg(&aux_dir)
@@ -557,6 +558,7 @@ impl<'test> TestCx<'test> {
         rustc
             .arg("-")
             .arg("-Zno-codegen")
+            .arg("-Zunstable-options")
             .arg("--out-dir")
             .arg(&out_dir)
             .arg(&format!("--target={}", target))